In an SpO2 transducer, light is generated by LEDs in response to pulse drive signals of substantially constant current through the LEDs. The optical signals produced by the LEDs are received by a photo-detector and converted to an electrical signal. The LEDs are sometimes conditioned to produce relatively low light levels (e.g. relatively low substantially constant current pulses). Under these operational conditions, it is possible for electronic (e.g. semiconductor) circuitry to induce sufficient noise in the driving pulse signals to become significant in subsequent generation of optical signals, and in reception and processing of the optical signals by the photo-detector. In addition, existing drive circuits draw pulses of current from a local power supply. The drawing of such pulses of current causes fluctuations in the power supply voltage output signal. These voltage fluctuations, in turn, induce corresponding fluctuations in signals within receiver circuitry, termed power supply crosstalk. Because of the timing of these disturbances, the receiver circuitry can incorrectly interpret them as representative of a received optical signal, thereby inducing a noise component into the received signal.